Now, to an abc news exclusive and a live report from inside iran, as they get ready to head into negotiations over the nuclear program with the u.S. And other nations. Abc's david muir has just arrived and joins us now from tehran. Good morning, david. Reporter: Robin, just to hear your voice, half a world away, enough to make us smile. The whole crew here, behind the camera, welcoming you back, even here in iran. As you mentioned, robin, it's a critical moment here. We're inside this country because u.S. Sanctions against this economy have crippled the economy here. And just days away, now, from iran returning to the negotiating table over its nuclear program. As you point out, in a rare move, they've allowed us in to report from the streets of tehran. This is a tenuous time here, just days before iran returns to the nuclear negotiating table with the u.S. And others, since talks collapsed eight months ago. This morning, as we drove through this city of 12 million, it is a city squeezed, not only by the traffic, but by the economic sanctions, led by the u.S. Some of the cars clogging these streets, tripling in price. It's groceries, medicine, if you're lucky enough to find it. As we were going into the subway, it is a proud republic, where the roles of men and women are still well defined. And the front car says women-only right here. Many say the currency is in a free-fall. And there's fears among many here that the economy is heading towards collapse. But will the sanctions work? Iran's supreme leader, ayatollah khamenei, speaking to americans just before the talks, telling the iranian people, we will not negotiate under pressure. The u.S. Is pointing a gun at iran and wants us to talk to them. The iranian nation will not be intimidated by these actions. Some very stern words there from the supreme leader. On a bit of a personal note here, I wanted to be one of the hundreds that tweeted you to welcome you back here. But a rude awakening here in iran because twitter is blocked in this country. Facebook, blocked. All social networking. It gives you an idea of how cohe message still is here in iran. My message comes from the heart, robin. Thank you very much. We're going to turn to washington now. And vice president joe biden unplugged. As part of his leading role in

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